This invention relates to an electromagnetic coupling such as a clutch or brake. More particularly, the invention relates to an electromagnetic coupling in which the active magnetic force is produced by a permanent magnet but is rendered ineffective upon energization of an associated winding.
A coupling of the foregoing general type is disclosed in Pierce U.S. Pat. No. 2,832,918. In that coupling, a permanent magnet creates flux which threads a working path between an armature and the concentric pole pieces of an annular shell in order to magnetically draw the armature into frictional engagement with the shell. A winding is concentric with the pole pieces and, upon being energized, creates flux which threads through the permanent magnet along a bypass path which is in parallel with the working path. When the winding is energized, the winding flux shunts the permanent magnet flux from the working path to the bypass path so as to render the permanent magnet ineffective and effect release of the armature from the pole pieces.